Aedes albopictus (Stegomyia albopicta), from the mosquito (Culicidae) family, also known as (Asian) tiger mosquito or forest mosquito, is a mosquito native to the tropical and subtropical areas of Southeast Asia; however, in the past few decades, this species has spread to many countries through the transport of goods and international travel.[1] It is characterized by the white bands on its legs and body.

Description

Name and systematics

In 1894, a British-Australian entomologist, Frederick A. Askew Skuse, was the first to scientifically describe the Asian tiger mosquito, which he named Culex albopictus (lat.culex "gnat", "midge" and albopictus "white-painted").[6][7] Later, the species was assigned to the genus Aedes (gr.άηδής, "unpleasant")[8] and referred to as Aedes albopictus.[9] Like the yellow fever mosquito, it belongs to the subgenus Stegomyia (Gr. στέγος, "covered, roofed", referring to the scales that completely cover the dorsal surface in this subgenus, and μυία, "fly") within the genus Aedes.[10] In 2004, scientists explored higher-level relationships and proposed a new classification within the genus Aedes and Stegomyia was elevated to the genus level, making Aedes albopictus now Stegomyia albopicta. This is, however, a controversial matter, and the use of Stegomyia albopicta versus Aedes albopictus is continually debated.[11][12][13]

Characteristics

Aedes albopictus

The Asian tiger mosquito is about 2 to 10 mm length with a striking white and black pattern.[6][14][15] The variation of the body size in adult mosquitoes depends on the density of the larval population and food supply within the breeding water. Since these circumstances are seldom optimal, the average body size of adult mosquitoes is considerably smaller than 10 mm. For example, the average length of the abdomen was calculated to be 2.63 mm, the wings 2.7 mm, and the proboscis 1.88 mm.[16]

The males are roughly 20% smaller than the females, but they are morphologically very similar. However, as in all mosquito species, the antennae of the males in comparison to the females are noticeably bushier and contain auditory receptors to detect the characteristic whine of the female. The maxillary palps of the males are also longer than their proboscis, whereas the females’ maxillary palps are much shorter. (This is typical for the males of the Culicinae.) In addition, the tarsus of the hind legs of the males is more silvery. Tarsomere IV is roughly 75% silver in the males whereas the females’ is only about 60% silver.

The other characteristics do not differentiate between sexes. A single silvery-white line of tight scales begins between the eyes and continues down the dorsal side of the thorax. This characteristic marking is the easiest and surest way to identify the Asian tiger mosquito.

The proboscis is dark colored, the upper surface of the end segment of the palps is covered in silvery scales, and the labium does not feature a light line on its underside. The compound eyes are distinctly separated from one another. The scute, the dorsal portion of an insect’s thoracic segment, is black alongside the characteristic white midline. On the side of the thorax, the scutellum, and the abdomen are numerous spots covered in white-silvery scales.

Such white-silvery scales can also be found on the tarsus, particularly on the hind legs that are commonly suspended in the air. The bases of tarsomeres I through IV have a ring of white scales, creating the appearance of white and black rings. On the fore legs and middle legs, only the first three tarsomeres have the ring of white scales, whereas tarsomere V on the hind legs is completely white. The femur of each leg is also black with white scales on the end of the “knee”. The femora of the middle legs do not feature a silver line on the base of the upper side, whereas, the femora on the hind legs have short white lines on base of the upper side. The tibiae are black on the base and have no white scales.

The terga on segments II through VI of the abdomen are dark and have an almost triangular silvery-white marking on the base that is not aligned with the silvery bands of scales on the ventral side of the abdomen. The triangular marking and the silvery band are only aligned on abdominal segment VII. The transparent wings have white spots on the base of the costae. With older mosquito specimens, the scales could be partially worn off, making these characteristics not stand out as much.[14][16]

The typical Ae. albopictus individual has a length around 2 to 10 mm.[15] As with other members of the mosquito family, the female is equipped with an elongated proboscis that she uses to collect blood to feed her eggs. The Asian tiger mosquito has a rapid bite that allows it to escape most attempts by people to swat it. By contrast, the male member of the species primarily feeds on nectar.

The female lays her eggs near water, not directly into it as other mosquitoes do, but typically near a stagnant pool. However, any open container containing water will suffice for larvae development, even with less than an ounce (30 ml) of water. It can also breed in running water, so stagnant pools of water are not its only breeding sites. It is more likely to lay eggs in water sources near flowers than in water sources without flowers. It has a short flight range (less than 200 m), so breeding sites are likely to be close to where this mosquito is found.[17][18]

Identifying tiger mosquitoes can seem easy with the above description, but many people mistakenly identify it. The best way to be sure is to compare the specimen with several approved pictures of the tiger mosquito.[19]

Similar species

Some mosquitoes in North America, such as
Ochlerotatus canadensis, have a similar leg pattern.

In Europe, the mosquito Culiseta annulata, which is very common, but does not occur in high densities, can be mistaken for an Asian tiger mosquito because of its black-and-white-ringed legs. However, this species is missing the distinctive white line that runs from the middle of its head and down the thorax. It is also considerably larger than Ae. albopictus, is not black and white, but rather beige and grey striped, and has wings with noticeable veins and four dark, indistinct spots.

In the eastern Mediterranean area, Ae. albopictus species can be mistaken for
Aedes cretinus, which also belongs to the subgenus Stegomyia and uses similar breeding waters. Aedes cretinus also has a white stripe on the scute, but it ends shortly before the abdomen, and also has two additional stripes to the left and right of the middle stripe. So far Aedes cretinus is only located in Cyprus, Greece, Macedonia, Georgia and Turkey.[20]

In Asia, the Asian tiger mosquito can be mistaken for other members of the subgenus Stegomyia, particularly the yellow fever mosquito Aedes aegypti (the most prevalent species in the tropics and subtropics), because both species display a similar black and white pattern. It can be hard to distinguish Ae. albopictus from the closely related Aedes scutellaris (India, Indonesia, Papua New Guinea, and the Philippines),
Aedes pseudoalbopictus (India, Indonesia, Malaysia, Myanmar, Nepal, Taiwan, Thailand, and Vietnam) and
Aedes seatoi (Thailand).[14][21]

Diet and host location

Bloated female at the end of a meal

Like other mosquito species, only the females require a blood meal to develop their eggs. Apart from that, they feed on nectar and other sweet plant juices just as the males do. In regards to host location, carbon dioxide and organic substances produced from the host, humidity, and optical recognition play important roles.

The search for a host takes place in two phases. First, the mosquito exhibits a nonspecific searching behavior until it perceives host stimulants, whereupon it secondly takes a targeted approach.[22] For catching tiger mosquitoes with special traps, carbon dioxide and a combination of chemicals that naturally occur in human skin (fatty acids, ammonia, and lactic acid) are the most attractive.[23]

The Asian tiger mosquito particularly bites in forests during the day, so has been known as the forest day mosquito. Depending upon region and biotype, activity peaks differ, but for the most part, they rest during the morning and night hours. They search for their hosts inside and outside of human dwellings, but are particularly active outside. The size of the blood meal depends upon the size of the mosquito, but it is usually around 2 μl. Their bites are not necessarily painful, but they are more noticeable than those from other kinds of mosquitoes. Tiger mosquitoes generally tend to bite a human host more than once if they are able to.[22][24]

Ae. albopictus also bites other mammals besides humans, as well as birds.[22][24] The females are always on the search for a host and are persistent but cautious when it comes to their blood meal and host location. Their blood meal is often broken off before enough blood has been ingested for the development of their eggs, so Asian tiger mosquitoes bite multiple hosts during their development cycle of the egg, making them particularly efficient at transmitting diseases. The mannerism of biting diverse host species enables the Asian tiger mosquito to be a potential bridge vector for certain pathogens that can jump species boundaries, for example the West Nile virus.

Toxorhynchites larvae, a mosquito genus that does not suck blood, feeds upon other mosquito larvae and are often found with tiger mosquito larvae. Flatworms and small swimming beetles are considered natural predators.[24]

Fungi from the genus Coelomomyces (order Blastocladiales) develop inside the visceral cavity of mosquito larvae. The species
Coelomomyces stegomyiae was first found on the Asian tiger mosquito.[24]

Paramecia, or ciliates, can also affect Ae. albopictus larvae, and the first detected species was
Lambornella stegomyiae (Hymenostomatida: Tetrahymenidae).[24] The virulence, mortality rate, and subsequent possibilities of Lambornella being implemented as a biological remedy to control Ae. albopictus, however, has conflicting views.[25][26]

Sporozoans of the genus Ascogregarina (Lecudinidae) infect the larval stage of mosquitoes. The species
Ascogregarina taiwanensis was found in Asian tiger mosquitoes.[24] When the adult mosquitoes emerge from their pupal case, they leave the infectious intermediary stage of parasites in the water and close off the infection cycle. Infected adults are generally smaller than non-infected adults and have an insignificantly higher mortality rate; therefore, food supply and larval density apparently play a role. In competitive situations, an infection with sporozoans can also reduce the biological fitness of other uninfected mosquitoes. However, the use of the parasites as an effective biological remedy to control mosquito populations is implausible because the host must reach the adult stage for the transmission of the parasites.[27]

Though they do not commonly occur in the natural habitats of Asian tiger mosquitoes, predatory copepods from the family Cyclopidae seem to willingly feed on them given the opportunity.[24] Relatives of different genera could therefore present a possibility in the control of tiger mosquitoes.[28]

Predators of adult Ae. albopictus in Malaysia include various spider species. Up to 90% of the gathered spiders from rubber plantations and a cemetery fed upon Asian tiger mosquitoes. Whether the spiders would have an effect on the mosquito population is still unclear. Tiger mosquitoes were abundantly present despite the existence of the spiders.[29]